The background art will refer to the disadvantages associated with reducing a conveyor length specifically associated with transporting run of mine coal from a longwall mining unit. However, this is for the purposes of explanation only and the invention is applicable to all types of belt conveyor systems where there is a need to adjust the length of the conveyor and there are problems associated with this which are similar to the problems found in a longwall mining method.
Traditionally, material extracted using the retreat longwall mining method is transported away from the mining unit using a belt conveyor. The belt conveyor consists of an endless belt, providing for upper carry and lower return belt strands which are supported by a system of idlers mounted by framework, with the idler and framework arrangement commonly referred to as “structure”.
The structure is made up of repeated units (modules) of fixed length, with each unit commonly referred to as a “bay”. Each bay of structure typically consists of the following major components:                H-frame—a transverse support stand comprising a horizontal cross member fitted with two vertical legs, to define an “H” configuration. The frame incorporates connection arrangements to mount stringers, bracing, a return idler set to support the return belt strand and a carry idler set (depending on the structure configuration) to support the carry belt strand;        Stringers—two fixed length spacer bars (one each side of the conveyor belt—that is the “walk” side and the “non-walk” side) connected to the H-frame legs to locate and support the H-frame at a regular interval (to suit conveyor belt support requirements), and depending on the structure configuration arrangement to mount carry idlers (to support the carry belt strand);        Bracing—two types of bracing including i) short rigid members connected between the H-frame legs and the stringers to provide stiffness to the H-frame to stringer connection, positioning the H-frame nominally perpendicular to the ground, and ii) longer rigid members connected diagonally between adjacent H-frame legs located on each end of a structure bay to ensure squareness of the structure bay;        Carry idler set—depending on the structure configuration, one or two catenary set(s) comprising of multiple individual idlers, mounted each end to either the upper part of the H-frame legs or the stringers respectively;        Return idler set—a catenary set comprising of multiple individual idlers, mounted each end to the lower part of the H-frame legs.        
The centreline of the conveyor belt structure is typically offset from the centreline of the underground roadway on which the structure is mounted thereby placing one side of the structure closer to one of the roadway walls. This results in the structure having a “non-walk” side (which is closest to the wall) and a “walk” side (where there is enough room between the structure and the opposing mine wall to allow passage of equipment and personnel). Even when not positioned adjacent a mine wall, it is common for a conveyor structure to have a walk side (which is safer to access) and a non-walk side (which should not be readily accessible).
For a longwall mining unit to retreat, the length of the conveyor structure needs to be reduced. This currently requires the structure to be dismantled and removed (recovered) to provide a clear path for the longwall bootend to travel. In the interests of practicality and efficiency, the structure must be recovered without cutting either of the conveyor belt strands. Therefore, the structure must be recovered from within the bounds of the conveyor belt strands.
A disadvantage is that the idler sets and stringers need to be disconnected and dismantled from both the walk side and non-walk side of the conveyor, which due to the proximity of personnel to moving conveyor components, presents a significant personal safety risk and requires the conveyor to be stopped.
The stopping of the conveyor belt means the mining unit cannot continue to mine coal, ceasing production.
Once a bay of structure has been dismantled, the components (located on the walk side, within the bounds of the conveyor belt strands and non-walk side of the conveyor) need to be manually moved to the walk side of the conveyor and away from the conveyor belt. A disadvantage is that to complete this activity safely, typically two mine personnel are required to handle the awkwardly shaped structure components, including the H-frame which may have a mass in excess of 50 kg.
Another disadvantage is that the activity of manually recovering the structure bay components provides a considerable risk to those mine personnel involved, through handling components of considerable mass and awkward shape, especially when considering the environment where the task occurs (often an uneven, wet floor in a poorly lit area).
Although the above description is provided for the case of reducing a conveyor length specifically associated with transporting run of mine coal from a longwall mining unit, it should be appreciated that the description is generally applicable for application in reverse (increasing length conveyor).
Any references to methods, apparatus or documents of the prior art are not to be taken as constituting any evidence or admission that they formed, or form part of the common general knowledge.
It is an object of the present invention to at least partially overcome or ameliorate one or more of the disadvantages of the prior art, or to provide a useful alternative.